1. Field of the Invention
The present invention relates to a water drop detector on a transparent substrate for detecting the presence of water drops present on a front surface of the transparent substrate by using a light emitting element and a light receiving element.
2. Description of Prior Art
Conventionally, as is described in Japanese Patent Laying-Open No. 2-67945 (1990), for example, there is already known a water drop detector apparatus for detecting water drops present on a windshield or other front window glass of a vehicle, which comprises a light emitting means including a light emitting element and so on and a light receiving means including a light receiving element and so on, wherein light is irradiated towards the windshield from the light emitting means, thereby determining that the water drops adhere only on the front surface of the windshield when an output signal from the light receiving means that receives the reflected light lies within a predetermined region of a level indicative of no adhesion of water drops, while determining that the water drops do adhere even on an interior surface of the windshield when the signal exceeds the predetermined region of the level indicative of no adhesion of water drops.
However, the water drop detector apparatus of the conventional art has drawbacks in that it may malfunction if any light coming from the outside enters directly into the light receiving means, and also in that the light from the light emitting means may go directly to the outside thereof, and further in that it has poor aesthetic appeal since a portion of the light receiving means can be seen from the outside thereof.